The invention relates to improvements in assemblies which can be utilized to take up and to compensate for shocks which develop as a result of fluctuations in the rotational speed of the output element of an internal combustion engine. More particularly, the invention relates to improvements in assemblies which can be used in motor vehicles between the internal combustion engine and the input element of a change-speed transmission to blunt the effects of shocks which develop as a result of fluctuations in the transfer of torque between the engine and the transmission. Still more particularly, the invention relates to improvements in assemblies of the type wherein a first rotary unit receives torque from the engine, a second rotary unit transmits torque to the transmission, the two units are coaxial with and rotatable within limits relative to each other, and the means for transmitting torque between the two units comprises a damper of vibrations and of other undesirable movements. As a rule, or at least in many instances, the damper comprises resilient elements which act in the circumferential direction of the two units and one or more friction generating devices.
Assemblies of the just outlined character are disclosed, for example, in German Offenlequngsschrift No. 29 26 012. The damping action between the two rotary units which can turn within limits with reference to one another is provided by energy storing devices in the form of coil springs and by a friction generating device which is installed to operate in parallel with the coil springs. The coil springs offer a progressively increasing resistance to further angular displacements of the two units with reference to each other from a starting or neutral position. In other words, the coil springs (or at least some of the coil springs) will yield in response to the exertion of a relatively small force when one of the units begins to move from the neutral position, and the resistance increases progressively as the angular displacement of the one unit relative to the other unit increases. The resistance which the friction generating device offers to rotation of the one unit relative to the other unit remains at least substantially constant.
Assemblies embodying the just described damper are designed to operate in such a way that their critical fundamental frequency, namely the critical RPM of the driven and driving parts, develops at a resonance which is below the ignition cycle frequency when the RPM of the engine is at a minimum value, namely the lowest RPM at which the engine is still running. However, when an internal combustion engine is started or turned off, it frequently takes a rather long period of time during which the RPM is within the critical range so that the vibration amplitude of the two units which are rotatable relative to each other increases still further as a result of excitation within such range of rotational speeds. The result is that the resilient elements of the damper between the two units undergo maximum deformation and enable rotation limiting stops on the two units to move into actual contact with each other. Under such circumstances, i.e., when the two stops actually abut against each other, the damper is totally ineffective in that it cannot compensate for or take up any shocks. Therefore, the vehicle which embodies such an assembly is vulnerable to shocks which develop while the two stops are in actual contact with one another due to the absence of any damping or shock absorbing action. This not only affects the comfort of the occupant or occupants of the motor vehicle but also generates pronounced noise. Still further, the shafts, bearings and certain other parts of the engine and transmission in the motor vehicle are likely to undergo substantial damage.